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A model reference approach to control induction motor drives is proposed. The robustness, against rotor time constant variation, is also assured. Reference is made to CRPWM inverter supply. Thus, a simple linear, time invariant and decoupled reference model is assumed. A non-linear controller which takes into account rotor time constant variation is synthesized resorting to the Lyapunov stability theory. Field oriented control is imposed to the reference model expressed in stator coordinates and computer simulation results are reported. The reference model and its control system has been implemented using operational amplifiers and integrated-circuits chips for generating special functions. The test results of the circuit are finally reported

In the paper, the torque control of an asynchronous motor fed by a voltage source inverter (VSI) is performed by evaluating, by means of a microprocessor, in each sampling interval the voltage space vector which gives rise to a mean value of the electromagnetic torque just equal to the imposed one. The correspondent modulation technique for the VSI is described. The results obtained by means of a numerical simulation show a very good behavior both in steady state and in transient operation, with particular reference to the accuracy and the quickness of the drive response.

An optimal use of microprocessors to control electric drives requires an approach which takes into account the peculiarities of digital control. The authors present the general structure of an electrical drive controlled by a microprocessor system, which makes it possible to exploit microprocessor performance. The main problems associated with digital control are analyzed. The corresponding output deviations are evaluated with reference to the asynchronous motor, starting from its mathematical model written in terms of symmetrical components.

The authors deal with some problems raised by the application of digital control to asynchronous motors. At first the mathematical model of a digitally controlled asynchronous motor is described, which allows a step by step evaluation of the main electrical and mechanical motor quantities. Then, it is used to evaluate currents and torqued ripples due to the digitalization of signals processing and numerical examples are shown for a sample asynchronous motor and for different feeding algorithms. It is finally shown that an easy analytical law exits between torque deviations and sampling period and that it can successfully be used for control designing purposes

A comparative analysis of asynchronous and brushless electric drives is performed, including as comparison terms the electromagnetic torque and its ratios both to the input currents and copper losses. The formulation of electromagnetic torque in a dynamic electromagnetic structure is reviewed. The generalised expression is then applied to different motor structures. >

The analysis of the alternative tourque components has always rapresented an important item for the evaluation of the characteristics and performances of inverter-fed asynchronous motors. The paper gives first a general methodology to evaluate the electromagnetic torques of asynchronous motors. The amplitudes of the alternative tourque components are then evaluated with reference both to the harmonic content of the currents and to the non-sinusoidal windings distribution. The paper is completed by a numerical example concerning the estimation of the alternative tourque components for different supply techniques.

The paper deals with real-time identification of the rotor parameters of the induction motor drive. The model reference adaptative control technique has been used for synthesising two identifiers. An appropriate choice of the reference model allows a Lyapunov function to be built by means of which the updating law of the rotor time constant can be found. A higher order identifier is also synthesised using the hyperstability approach which allows real-time updating of two rotor parameters. The persistent exciting property of the input vector assures the parameters convergence. Using a DSP-based system (TMS320C30), having 30 MHz clock frequency, a few experiments are conducted for testing the proposed identifiers performance in the case of a CRPWM inverter supplied drive.

In this paper an high performances serial bus for electrical drive synchronization is proposed and tested. The main targets of the proposed bus are: switching pattern synchronization; closing of currents loops; interfacing of digital encoders. Experimental tests confirm the feasibility of the proposed bus

The paper describes a vectorial control strategy for induction motor fed by VSI which allows to exploit the dynamic performances by taking into account both the rotor and stator time constant, and avoiding at the same time the use of current control loop. It is based on the step-by-step evaluation of the feeding voltage of the motor, in such a way as to achieve the imposed space vector of the stator current, corresponding to the reference values of the electromagnetic torque and flux. The strategy has been implemented on fully DSP-based control architecture for speed control of an induction motor drive. Experimental results are presented and compared with the ones obtained with an hysteresis current control loop. They show a very good behaviour of the system, both in dynamic and steady-state operating conditions.

With reference to speed controlled induction motor, an algorithm which allows the on-line estimation either of the speed and one motor parameter or, alternatively, of two motor parameters, is described in the paper. Simulation results fully confirm the validity of the proposed algorithm.

This paper analyzes the sensitivity of the electromagnetical efficiency with respect to the electrical parameter variations for a series of standard three-phase asynchronous motors. At first, the electromagnetical efficiency of asynchronous motors is determined by referring to the electrical equivalent circuit of the motor; iron and copper losses are only considered. Then, the expression of the ratios between the p.u. variation of the efficiency and the p.u. variation of each electrical parameter are given either for fixed speeds or for fixed effective values of the stator phase current. Besides the p.u. variations of the efficiency are related to the contemporaneous p.u. variations of all electrical parameters by means of a simple relation.

Field oriented control of induction motor drives needs the detection of rotor flux which is usually detected by means of an observer. Rotor time constant variation due to rotor heating de-tunes the observer and, hence, the field oriented control. In the present paper an adaptive observer is synthesized, which allows the on-line rotor time constant tuning. The identification of the rotor time constant is performed by a model reference approach. The synthesis of the adaptive observer is conducted using the Lyapunov stability theory applied to the drive-observer system. The simulation results evidence the good performance of the proposed observer and, hence, of the overall controlled drive. In particular, the interactive effects between the observer and the parameter identifier gains is evidenced.

A general approach to direct torque and flux control of an induction motor fed by a VSI is presented in the paper. The inverter switching patterns are generated as a function of the reference values of both the electromagnetic torque and of the controlled flux. In particular, the proposed control algorithm is independent of which kind of flux is controlled-rotor or stator. The results obtained by means of a real-time simulation show that the proposed control strategy allows very fast and accurate response of the drive A general approach to direct torque and flux control of an induction motor fed by a VSI is presented in the paper. The inverter switching patterns are generated as a function of the reference values of both the electromagnetic torque and of the controlled flux. In particular, the proposed control algorithm is independent of which kind of flux is controlled-rotor or stator. The results obtained by means of a real-time simulation show that the proposed control strategy allows very fast and accurate response of the drive

Single-phase asynchronous capacitor motors are discussed. Conventional and renewed two- and three-windings stators are considered. For both types a general mathematical model is suggested and experimentally validated. This model is suitable for the determination of optimized operating conditions. Some of these conditions are considered together with numerical solutions for several examples

In power converters, PWM techniques generally offer acceptable spectral shapes for load currents only if high switching frequencies are adopted. In medium-high power applications, in order to reduce the EMI and commutation losses, the basic goal of the modulation strategies must be the minimization of the harmonic distortion by keeping, at the same time, the switching frequency to a low value. In this paper, this feature is achieved for an ac drives by adopting a front-end inverter structures. In fact, the possibility of achieving variable dc link voltages allows to perform an optimization procedure which drastically reduce the motor current harmonics working with very low value of the switching frequency. The proposed technique has been validated by means of an experiment analysis and a performance comparison with a traditional space vector modulation technique. A full EMC analysis is also performed to evaluate radiated and conducted emissions.

A control strategy which allows to impose the re-adhesion trajectory in electrical drives for traction purposes is described in the paper. It is based on the imposition of the mechanical response of the drive. In particular, the standard regulator of the external speed loop is replaced by imposing the desired dynamic response of the drive corresponding to an assigned reference speed.

A novel approach to the torque control both in constant torque region, and in the field-weakening one of permanent magnet AC machines drives fed by VSI, is described in this paper. It is based on the prediction of all the possible transient responses of the drive, in terms of torque and flux, to the available output voltages of the voltage source inverter feeding the motor. Experimental results confirms the validity of the proposed approach and the possibility of achieving very good dynamic performances.